1. Field of the Invention
The present invention is related to a heat exchanger mounted on a motorcycle and to a manufacturing method thereof. The present invention is effectively applied to a radiator, for motorcycle use, for cooling cooling water circulated in an internal combustion engine.
2. Description of the Related Art
FIG. 1 is a front view showing a conventional radiator 1 for motorcycle use. Usually, the radiator 1 includes tubes 2, fins 3, header tanks 4 and so forth. Concerning the structure of the conventional radiator, refer to the official gazette of JP-A-2001-1970.
In this connection, the radiator is conventionally fixed to a vehicle as follows. A through-hole is formed in a bracket provided in the radiator. After a rubber grommet and a collar have been attached to the through-hole, a frame of the vehicle is engaged in the through-hole via the grommet and collar so that the radiator can be fixed to the vehicle.
In the case of a motorcycle used for motocross racing which requires a high vibration-proof property, as shown in FIG. 7, a burring portion J81 is formed in an inner circumferential edge portion J80a of a through-hole J80 by the working of burring, so that a contact area of the grommet J9 with the inner circumferential portion J80a of the through-hole J80 can be magnified and the vibration-proof property can be enhanced.
However, in the above radiator for motorcycle use which is used for motocross racing, the following problems may be encountered. At the time of forming the burring portion J81, as shown in FIG. 8, a forward end portion J81a of the burring portion J81 is ironed by the working of burring and formed into a sharp shape. Therefore, when the burring portion J81 and the grommet J9 are rubbed with each other, the sharp forward end portion J81a shaves the grommet J9. Accordingly, there is a possibility that the grommet J9 is ruptured. When the grommet J9 is ruptured, high intensity vibration is transmitted from the vehicle to the radiator. Accordingly, there is a possibility that the radiator may be broken.